The present invention relates to a disc brake including a torque-carrying plate having a torque-carrying surface of improved design so that it can support an inner pad stably until it is completely worn out even if the torque-carrying plate is thinner than conventional plates.
Known floating-caliper type disc brakes include one type in which its inner pad, biased by a brake piston, is in abutment with a fixed torque-carrying plate so that the brake torque applied to the inner pad is carried on the torque-carrying plate, whereas the outer pad is fixed to the outer portion of the caliper so that the brake torque applied to the outer pad is carried on the caliper.
In this type of disc brake, if at the start of use of the pad the entire torque-transmission surface formed on the backing plate of the inner pad is in contact with the torque-carrying surface (if not, that is, if the torque is transmitted not through the entire torque-transmission surface but only through part of it, the torque-carrying surface and the torque-transmission surface tend to be damaged), the width (in the axial direction of the disc) of the torque-carrying surface of the torque-carrying plate has to be determined by taking into account the sliding amount of the inner pad when it is completely worn out. Otherwise, when the inner pad has been completely worn out, it will come off of the torque-carrying plate, so that a large load will act on pad pins which support the pads so as to be slidable in the axial direction of the disc. If the inner pad is supported on the torque-carrying plate, it will drop off, so that the disc brake will completely lose its braking function.
For the above reasons, the torque-carrying plate has to be sufficiently thick so that it can support even a pad that has been completely worn out.
Such a torque-carrying plate is formed by blanking a steel plate because blanking is better in terms of mass-productivity than casting. The thinner the blanked plate, the more easily it can be machined. Also, the thinner the torque-carrying plate, the smaller the total weight of the disc brake.
But in conventional disc brakes of this type, since the width of the torque-carrying surface is equal to the thickness of the torque-carrying plate, it is impossible to reduce the thickness of the plate below a certain point. Also, since thicknesses of the blanked plates tend to vary at their edges, that is, they have an inaccuracy in size, it is necessary to correct such inaccuracies by machining so that the torque-carrying surface has a sufficient width. This machining work is troublesome. The torque-carrying plates thus obtained are not light enough.